Emission-line properties of Seyfert 2 nuclei

We use two volume-limited active galactic nucleus (AGN) host galaxy samples constructed by Deng & Wen [47], and explore the environmental dependence of the stellar velocity dispersion in these two volume-limited AGN host galaxy samples. In the luminous volume-limited AGN host galaxy sample, the stellar velocity dispersion of AGN host galaxies apparently depends on local environments: AGN host galaxies with large stellar velocity dispersion exist preferentially in high density regime, while AGN host galaxies with small stellar velocity dispersion are located preferentially in low density regions. But in the faint volume-limited AGN host galaxy sample, this dependence is fairly weak. We also examine the dependence of the clustering properties of AGN host galaxies on the stellar velocity dispersion by cluster analysis, and find that in the luminous volume-limited AGN host galaxy sample, AGN host galaxies with small stellar velocity dispersion preferentially form isolated galaxies, close pairs and small groups, while AGN host galaxies with large stellar velocity dispersion preferentially inhabit the dense groups and clusters. In the faint volume-limited AGN host galaxy sample, although the fraction of isolated galaxies with small stellar velocity dispersion is apparently higher than the one with large stellar velocity dispersion, the trend in the luminous volume-limited sample is very difficultly observed. This likely is due to the galaxy number of the faint volume-limited AGN host galaxy sample being too small to ensure an ideal statistical analysis.

In this work, we publish stellar velocity dispersions, sizes, and dynamical masses for eight ultramassive galaxies (UMGs; > 11), z ≳ 3) from the Massive Ancient Galaxies At z > 3 NEar-infrared (MAGAZ3NE) Survey, more than doubling the number of such galaxies with velocity dispersion measurements at this epoch. Using the deep Keck/MOSFIRE and Keck/NIRES spectroscopy of these objects in the H and K bandpasses, we obtain large velocity dispersions of ∼400 km s−1 for most of the objects, which are some of the highest stellar velocity dispersions measured and ∼40% larger than those measured for galaxies of similar mass at z ∼ 1.7. The sizes of these objects are also smaller by a factor of 1.5–3 compared to this same z ∼ 1.7 sample. We combine these large velocity dispersions and small sizes to obtain dynamical masses. The dynamical masses are similar to the stellar masses of these galaxies, consistent with a Chabrier initial mass function (IMF). Considered alongside previous studies of massive quiescent galaxies across 0.2 < z < 4.0, there is evidence for an evolution in the relation between the dynamical mass–stellar mass ratio and velocity dispersion as a function of redshift. This implies an IMF with fewer low-mass stars (e.g., Chabrier IMF) for massive quiescent galaxies at higher redshifts in conflict with the bottom-heavy IMF (e.g., Salpeter IMF) found in their likely z ∼ 0 descendants, though a number of alternative explanations such as a different dynamical structure or significant rotation are not ruled out. Similar to data at lower redshifts, we see evidence for an increase of IMF normalization with velocity dispersion, though the z ≳ 3 trend is steeper than that for z ∼ 0.2 early-type galaxies and offset to lower dynamical-to-stellar mass ratios.

ABSTRACTWe investigate the mean locally measured velocity dispersions of ionized gas (σgas) and stars (σ*) for 1090 galaxies with stellar masses $\log \, (M_{\!\ast }/M_{\odot }) \ge 9.5$ from the SAMI Galaxy Survey. For star-forming galaxies, σ* tends to be larger than σgas, suggesting that stars are in general dynamically hotter than the ionized gas (asymmetric drift). The difference between σgas and σ* (Δσ) correlates with various galaxy properties. We establish that the strongest correlation of Δσ is with beam smearing, which inflates σgas more than σ*, introducing a dependence of Δσ on both the effective radius relative to the point spread function and velocity gradients. The second strongest correlation is with the contribution of active galactic nuclei (AGN) (or evolved stars) to the ionized gas emission, implying that the gas velocity dispersion is strongly affected by the power source. In contrast, using the velocity dispersion measured from integrated spectra (σap) results in less correlation between the aperture-based Δσ (Δσap) and the power source. This suggests that the AGN (or old stars) dynamically heat the gas without causing significant deviations from dynamical equilibrium. Although the variation of Δσap is much smaller than that of Δσ, a correlation between Δσap and gas velocity gradient is still detected, implying that there is a small bias in dynamical masses derived from stellar and ionized gas velocity dispersions.

To constrain the nature and fraction of the ionized gas outflows in active galactic nuclei (AGNs), we perform a detailed analysis on gas kinematics as manifested by the velocity dispersion and shift of the λ5007 emission line, using a large sample of ∼39,000 type 2 AGNs at z &lt; 0.3. First, we confirm a broad correlation between and stellar velocity dispersions, indicating that the bulge gravitational potential plays a main role in determining the kinematics. However, velocity dispersion is on average larger than stellar velocity dispersion by a factor of 1.3–1.4 for AGNs with double Gaussian , suggesting that the non-gravitational component, i.e., outflows, is almost comparable to the gravitational component. Second, the increase of the velocity dispersion (after normalized by stellar velocity dispersion) with both AGN luminosity and Eddington ratio suggests that non-gravitational kinematics are clearly linked to AGN accretion. The distribution in the velocity–velocity dispersion diagram dramatically expands toward large values with increasing AGN luminosity, implying that the launching velocity of gas outflows increases with AGN luminosity. Third, the majority of luminous AGNs present the non-gravitational kinematics in the profile. These results suggest that ionized gas outflows are prevalent among type 2 AGNs. On the other hand, we find no strong trend of the kinematics with radio luminosity, once we remove the effect of the bulge gravitational potential, indicating that ionized gas outflows are not directly related to radio activity for the majority of type 2 AGNs.

The rate of tidal disruption events (TDEs), , is predicted to depend on stellar conditions near the super-massive black hole (SMBH), which are on difficult-to-measure sub-parsec scales. We test whether depends on kpc-scale global galaxy properties, which are observable. We concentrate on stellar surface mass density, , and velocity dispersion, , which correlate with the stellar density and velocity dispersion of the stars around the SMBH. We consider 35 TDE candidates, with and without known X-ray emission. The hosts range from star-forming to quiescent to quiescent with strong Balmer absorption lines. The last (often with post-starburst spectra) are overrepresented in our sample by a factor of or , depending on the strength of the Hδ absorption line. For a subsample of hosts with homogeneous measurements, – , higher on average than for a volume-weighted control sample of Sloan Digital Sky Survey galaxies with similar redshifts and stellar masses. This is because (1) most of the TDE hosts here are quiescent galaxies, which tend to have higher than the star-forming galaxies that dominate the control, and (2) the star-forming hosts have higher average than the star-forming control. There is also a weak suggestion that TDE hosts have lower than for the quiescent control. Assuming that , and applying a statistical model to the TDE hosts and control sample, we estimate and . This is broadly consistent with being tied to the dynamical relaxation of stars surrounding the SMBH.

We apply the stellar population synthesis code by Cid Fernandes et al. to model the stellar contribution for a sample of 209 type II AGNs at $0.3<z<0.83$ from the Sloan Digital Sky Survey. The reliable stellar velocity dispersions ($\sigma_{*}$) are obtained for 33 type II AGNs with significant stellar absorption features. According to the $L_{\rm [O III]}$ criterion of $3\times 10^{8} \Lsolar$, 20 of which can be classified as type II quasars. We use the formula of Greene & Ho to obtain the corrected stellar velocity dispersions ($\sigma_{*}^c$). We also calculate the supermassive black holes masses from $\sigma_{*}^c$ in these high-redshift type II AGNs. The [O III] luminosity is correlated with the black hole mass (although no correlation between the extinction-corrected [O III] luminosity and the black hole mass), and no correlation is found between the Eddington ratio and the [O III] luminosity or the corrected [O III] luminosity. Three sets of two-component profile are used to fit multiple emission transitions ([O III]$\lambda\lambda$4959, 5007 and [O II]$\lambda\lambda$3727, 3729) in these 33 stellar-light subtracted spectra. We also measure the gas velocity dispersion ($\sigma_{g}$) from these multiple transitions, and find that the relation between $\sigma_{g}$ and $\sigma_{*}^c$ becomes much weaker at higher redshifts than in smaller redshifts. The distribution of $<\sigma_{g}/\sigma_{*}^c>$ is $1.24\pm0.76$ for the core [O III] line and $1.20\pm0.96$ for the [O II] line, which suggests that $\sigma_{g}$ of the core [O III] and [O II] lines can trace $\sigma_{*}^c$ within about 0.1 dex in the logarithm of $\sigma_{*}^c$. For the secondary driver, we find that the deviation of $\sigma_{g}$ from $\sigma_{*}^c$ is correlated with the Eddington ratio.

We investigated the stellar velocity dispersion functions (VDFs) of pressure-supported galaxies in the EAGLE cosmological simulations. The central stellar velocity dispersion is one of the fundamental dynamical tracers of the total mass of galaxy subhalos, alongside luminosity and stellar mass. Because it reflects the gravitational potential, the stellar velocity dispersion is expected to be relatively insensitive to feedback from active galactic nuclei (AGNs), a critical process that regulates the connection between other galaxy observables and subhalo masses. To examine the impact of AGN feedback, we analyzed the VDFs from five EAGLE simulation runs, each adopting a different AGN feedback model: one "standard", two "enhanced", one "reduced," and one with no AGN feedback. We computed the stellar velocity dispersions of pressure-supported galaxies using member stellar particles, mimicking fiber spectroscopy. The VDFs from the standard and enhanced AGN feedback models show little difference. However, contrary to our initial expectation that the VDF shape would be largely insensitive to AGN feedback, the simulations with reduced and no AGN feedback show a significant excess of high velocity dispersion galaxies (σ_ * &gt; 200 ̨ms) and a deficit of low velocity dispersion galaxies (100 &lt; σ_ * (̨ms) &lt; 200), compared to those with standard or enhanced AGN feedback. The presence of high velocity dispersion galaxies in the no-AGN model arises from enhanced central star formation, due to the absence of AGN-driven gas heating or expulsion. Our results demonstrate that the shape of the theoretical VDF is sensitive to the strength of AGN feedback. These predictions offer a theoretical benchmark for future observational studies of the galaxy VDF using large-scale spectroscopic surveys.

We have compiled a sample of 2728 nearby (z &lt; 0.08) elliptical galaxies with photometry in the g, r, i, z bands from the Sloan Digital Sky Survey (SDSS) and J, H, K photometry from the Two-Micron All-Sky Survey (2MASS). Stellar masses, stellar velocity dispersions and structural parameters such as sizes and surface mass densities are also available for these objects. In order to correct the aperture mismatch between SDSS and 2MASS, we correct the SDSS magnitudes to the isophotal circular radius where the 2MASS magnitudes are measured. We compare the correlations between optical, optical-infrared and infrared colours and galaxy luminosity, stellar mass, velocity dispersion and surface mass density. We find that all galaxy colours correlate more strongly with stellar mass and velocity dispersion than with any other structural parameter. The dispersion about these two relations is also smaller. We also study the correlations between a variety of stellar absorption-line indices and the same set of galaxy parameters and we reach very similar conclusions. Finally, we analyse correlations between absorption-line indices and colour. Our results suggest that the optical colours of elliptical galaxies are sensitive to a combination of age, metallicity and alpha-enhancement, while the optical-infrared colours are sensitive to metallicity and to alpha-enhancement, but are somewhat less sensitive to age.

We use principal component analysis (PCA) to estimate stellar masses, mean stellar ages, star formation histories (SFHs), dust extinctions and stellar velocity dispersions for ~290,000 galaxies with stellar masses greater than $10^{11}Msun and redshifts in the range 0.4<z<0.7 from the Baryon Oscillation Spectroscopic Survey (BOSS). We find the fraction of galaxies with active star formation first declines with increasing stellar mass, but then flattens above a stellar mass of 10^{11.5}Msun at z~0.6. This is in striking contrast to z~0.1, where the fraction of galaxies with active star formation declines monotonically with stellar mass. At stellar masses of 10^{12}Msun, therefore, the evolution in the fraction of star-forming galaxies from z~0.6 to the present-day reaches a factor of ~10. When we stack the spectra of the most massive, star-forming galaxies at z~0.6, we find that half of their [OIII] emission is produced by AGNs. The black holes in these galaxies are accreting on average at ~0.01 the Eddington rate. To obtain these results, we use the stellar population synthesis models of Bruzual & Charlot (2003) to generate a library of model spectra with a broad range of SFHs, metallicities, dust extinctions and stellar velocity dispersions. The PCA is run on this library to identify its principal components over the rest-frame wavelength range 3700-5500A. We demonstrate that linear combinations of these components can recover information equivalent to traditional spectral indices such as the 4000A break strength and HdA, with greatly improved S/N. This method is able to recover physical parameters such as stellar mass-to-light ratio, mean stellar age, velocity dispersion and dust extinction from the relatively low S/N BOSS spectra. We examine the sensitivity of our stellar mass estimates to the input parameters in our model library and the different stellar population synthesis models.

The main objective of this article is to check the Unified Model (UM) for the expected similar stellar velocity dispersions between Type 1 and Type 2 active galactic nuclei (AGNs) and then to provide further clues on black hole (BH) mass properties. Unlike previous comparisons of BH masses estimated from M BH–σ relations for Type 2 AGNs and from virial BH masses for Type 1 AGNs, reliable stellar velocity dispersions σ measured from absorption features around 4000 Å are directly compared between the thus far largest samples of 6260 low-redshift (z < 0.3) Type 1 AGNs and almost all Type 2 AGNs in SDSS DR12. Although half of Type 1 AGNs do not have a measured σ due to unapparent absorption features overwhelmed by AGN activities, both properties of the mean spectra of Type 1 AGNs with and without a measured σ and a positive dependence of σ on the [O iii] luminosity can lead to a statistically larger σ for all Type 1 AGNs compared to the 6260 Type 1 AGNs with measured stellar velocity dispersions. Then, direct σ comparisons can lead to a statistically larger σ in Type 1 AGNs, with a confidence level higher than 10σ, after considering the necessary effects of different redshifts and different central AGN activities. Although Type 1 AGNs have a σ of only about (9 ± 3)% larger than Type 2 AGNs, the difference cannot be well explained at the current stage. Unless there is strong evidence to support different M BH–σ relations or to support quite different evolutionary histories between Type 1 and Type 2 AGNs, the statistically larger σ in Type 1 AGNs provides a strong challenge to the UM of AGNs.

The cumulative comoving number-density of galaxies as a function of stellar mass or central velocity dispersion is commonly used to link galaxy populations across different epochs. By assuming that galaxies preserve their number-density in time, one can infer the evolution of their properties, such as masses, sizes, and morphologies. However, this assumption does not hold in the presence of galaxy mergers or when rank ordering is broken owing to variable stellar growth rates. We present an analysis of the evolving comoving number density of galaxy populations found in the Illustris cosmological hydrodynamical simulation focused on the redshift range $0\leq z \leq 3$. Our primary results are as follows: 1) The inferred average stellar mass evolution obtained via a constant comoving number density assumption is systematically biased compared to the merger tree results at the factor of $\sim$2(4) level when tracking galaxies from redshift $z=0$ out to redshift $z=2(3)$; 2) The median number density evolution for galaxy populations tracked forward in time is shallower than for galaxy populations tracked backward in time; 3) A similar evolution in the median number density of tracked galaxy populations is found regardless of whether number density is assigned via stellar mass, stellar velocity dispersion, or dark matter halo mass; 4) Explicit tracking reveals a large diversity in galaxies' assembly histories that cannot be captured by constant number-density analyses; 5) The significant scatter in galaxy linking methods is only marginally reduced by considering a number of additional physical and observable galaxy properties as realized in our simulation. We provide fits for the forward and backward median evolution in stellar mass and number density and discuss implications of our analysis for interpreting multi-epoch galaxy property observations.

We employ a bias-corrected abundance matching technique to investigate the coevolution of the LCDM dark halo mass function (HMF), the observationally derived velocity dispersion and stellar mass functions (VDF, SMF) of galaxies between z=1 and 0. We use for the first time the evolution of the VDF constrained through strong lensing statistics by Chae (2010) for galaxy-halo abundance matching studies. As a local benchmark we use a couple of z ~ 0 VDFs (a Monte-Carlo realised VDF based on SDSS DR5 and a directly measured VDF based on SDSS DR6). We then focus on connecting the VDF evolution to the HMF evolution predicted by N-body simulations and the SMF evolution constrained by galaxy surveys. On the VDF-HMF connection, we find that the local dark halo virial mass-central stellar velocity dispersion (Mvir-sigma) relation is in good agreement with the individual properties of well-studied low-redshift dark haloes, and the VDF evolution closely parallels the HMF evolution meaning little evolution in the Mvir-sigma relation. On the VDF-SMF connection, it is also likely that the stellar mass-stellar velocity dispersion (Mstar-sigma) relation evolves little taking the abundance matching results together with other independent observational results and hydrodynamic simulation results. Our results support the simple picture that as the halo grows hierarchically, the stellar mass and the central stellar velocity dispersion grow in parallel. We discuss possible implications of this parallel coevolution for galaxy formation and evolution under the LCDM paradigm.

We have measured gas and stellar velocity dispersions in five circumnuclear star-forming regions (CNSFRs) and the nucleus of the barred spiral galaxy NGC 3351. The stellar dispersions have been obtained from high-resolution spectra of the Ca II triplet (CaT) lines at λλ8494, 8542, 8662 A, while the gas velocity dispersions have been measured by Gaussian fits to the Hβ λ4861 A line on high-dispersion spectra. The CNSFRs, with sizes of about 100 to 150pc in diameter, are seen to be composed of several individual star clusters with sizes between 1.7 and 4.9 pc on a Hubble Space Telescope (HST) image. Using the stellar velocity dispersions, we have derived dynamical masses for the entire star-forming complexes and for the individual star clusters. Values of the stellar velocity dispersions are between 39 and 67 km s -1 . Dynamical masses for the whole CNSFRs are between 4.9 x 106 and 4.3 x 10 7 M ⊙ and between 1.8 and 8.7 x 10 6 M ⊙ for the individual star clusters. Stellar and gas velocity dispersions are found to differ by about 20kms -1 with the Hβ lines being narrower than both the stellar lines and the [O III]λ5007 A lines. We have found indications for the presence of two different kinematical components in the ionized gas of the regions. The radial velocity curve shows deviation from circular motions for the ionized hydrogen consistent with its infall towards the central regions of the galaxy at a velocity of about 25 km s -1 . To disentangle the origin of these two components it will be necessary to map these regions with high spectral and spatial resolution and much better signal-to-noise ratio in particular for the O 2+ lines.

Maintenance-mode feedback from low-accretion-rate active galactic nuclei (AGNs), manifesting itself observationally through radio-loudness, is invoked in all cosmological galaxy formation models as a mechanism that prevents excessive star formation in massive galaxies (M * ≳ 3 × 1010 M ⊙). We demonstrate that at a fixed mass the incidence of radio-loud (RL) AGNs (L &gt; 1023 W Hz−1) identified in the Faint Images of the Radio Sky at Twenty centimeter and NRAO Very Large Array Sky Survey radio surveys among a large sample of quiescent (non-star-forming) galaxies selected from the Sloan Digital Sky Survey is much higher in geometrically round galaxies than in geometrically flat, disk-like galaxies. As found previously, the RL AGN fraction increases steeply with stellar velocity dispersion σ * and stellar mass, but even at a fixed velocity dispersion of 200–250 km s−1 this fraction increases from 0.3% for flat galaxies (projected axis ratio of q &lt; 0.4) to 5% for round galaxies (q &gt; 0.8). We rule out the hypothesis that this strong trend is due to projection effects in the measured velocity dispersion. The large fraction of RL AGNs in massive, round galaxies is consistent with the hypothesis that such AGNs deposit energy into their hot gaseous halos, preventing cooling and star formation. However, the absence of such AGNs in disk-like quiescent galaxies—most of which are not satellites in massive clusters, raises important questions. Is maintenance-mode feedback a generally valid explanation for quiescence? If so, how does that feedback avoid manifesting at least occasionally as an RL galaxy?

The dominant physical formation mechanism(s) for ultradiffuse galaxies (UDGs) is still poorly understood. Here, we combine new, deep imaging from the Jeanne Rich Telescope with deep integral field spectroscopy from the Keck II telescope to investigate the formation of UDG1137+16 (dw1137+16). Our new analyses confirm both its environmental association with the low density UGC 6594 group, along with its large size of 3.3 kpc and status as a UDG. The new imaging reveals two distinct stellar components for UDG1137+16, indicating that a central stellar body is surrounded by an outer stellar envelope undergoing tidal interaction. Both the components have approximately similar stellar masses. From our integral field spectroscopy, we measure a stellar velocity dispersion within the half-light radius (15 ± 4 km s−1) and find that UDG1137+16 is similar to some other UDGs in that it is likely dark matter dominated. Incorporating literature measurements, we also examine the current state of UDG observational kinematics. Placing these data on the central stellar velocity dispersion–stellar mass relation, we suggest there is little evidence for UDG1137+16 being created through a strong tidal interaction. Finally, we investigate the constraining power current dynamical mass estimates (from stellar and globular cluster velocity dispersions) have on the total halo mass of UDGs. As most are measured within the half-light radius, they are unable to accurately constrain UDG total halo masses.